High density polyethylene is a plastic commonly used to make water pipes and fittings. Relative to pipe made from various metals and metal alloys, high density polyethylene has the advantages of being light, easy to mold, and inexpensive. However, in long term use pipes and fittings made from high density polyethylene can be chemically attacked by chlorine and chlorine derivatives that are either naturally occurring or intentionally added to water supplies. There is therefore a desire for high density polyethylene pipes and fitting with greater resistance to chlorine and chlorine derivatives.